115.359. 1. Any person who has filed a declaration of candidacy for nomination and who wishes to withdraw as a candidate shall, not later than the eleventh Tuesday prior to the primary election, file a written, sworn statement of withdrawal in the office of the official who accepted such candidate’s declaration of candidacy. Any person nominated for an office who wishes to withdraw as a candidate shall, not later than the eleventh Tuesday prior to the general election, file a written, sworn statement of withdrawal in the office of the official who accepted such candidate’s declaration of candidacy. In addition, any person who has filed a declaration of candidacy for nomination or who is nominated for an office who wishes to withdraw as a candidate due to being named as the party candidate for a different office by a party nominating committee pursuant to sections 115.363 to 115.377 may withdraw as a candidate no later than 5:00 p.m. on the fifth day after being named as the party candidate for a different office by the party nominating committee.

Conservatives are split as to whether Akin should withdraw (see, e.g., here and here).

Meanwhile, polling analyst Nate Silver is estimating that Akin’s remarks will result in a 10-point shift in the polls:

If Mr. Akin lost a net of 10 points in the polls to Ms. McCaskill because of the remark, he would be trailing her by five points in surveys rather than leading her by about that margin.

It can be easy to overrate the importance of scandals in the first few days after they occur. Many voters will vote along party lines almost no matter what, and others will decide based on factors like the economy or an incumbent senator’s voting record.

Nevertheless, my view is that insensitive comments concerning rape are especially likely to be deemed inexcusable by voters, and that the swing against Mr. Akin could be larger than the average of 10 percentage points from similar events.